Method for producing a thermoplastic moulding compound

Abstract

A method for producing a thermoplastic moulding compound by means of an extruder (10), which comprises at least one feed zone (20), at least one mixing section (30), at least one venting section (40) and at least one discharge zone (50), wherein in the at least one feed zone (20) a water-containing first component and a second component are supplied, in the at least one mixing section (30) the thermoplastic moulding compound is mixed and contained water is evaporated, in the at least one venting section (40) water vapour is removed from the moulding compound and in the at least one discharge zone (50) the moulding compound is discharged. At least one of the mixing housings (31, 32) is kept at a temperature that is equal to or lower than the temperature of the moulding compound within the mixing section (30).

Claims

1. A process for producing a thermoplastic molding composition by an extruder, comprising: at least one feed zone, at least one mixing section, at least one venting section, and at least one discharge zone, wherein: a water-containing first component of the thermoplastic molding composition and a second component of the thermoplastic molding composition are introduced in the at least one feed zone, the thermoplastic molding composition is mixed and water present is evaporated in the at least one mixing section, water vapor is removed from the thermoplastic molding composition in the at least one venting section, and the thermoplastic molding composition is discharged in the at least one discharge zone, and wherein: at least one mixing barrel section of the mixing section is maintained at a temperature which is the same as or lower than the temperature of the thermoplastic molding composition within the mixing section, a first mixing barrel section and/or a second mixing barrel section is/are operated adiabatically, and at least one barrel section of the venting section is heated by temperature-control equipment in a manner such that the temperature of the at least one barrel section of the venting section is higher than the temperature of at least one mixing barrel section, and/or at least one barrel section of the discharge zone is heated by temperature-control equipment in a manner such that the temperature of the at least one barrel section of the discharge zone is higher than the temperature of at least one mixing barrel section.

2. The process of claim 1, wherein the temperature at which at least one mixing barrel section is maintained is lower by at least 10 K than the temperature of the thermoplastic molding composition within the mixing section.

3. The process of claim 1, wherein at least one barrel section of the feed zone is heated by temperature-control equipment in a manner such that the temperature of the at least one barrel section of the feed zone is higher than the temperature of at least one mixing barrel section.

4. The process of claim 1, wherein the water-containing first component of the thermoplastic molding composition and the second component of the thermoplastic molding composition are introduced together in the feed zone.

5. The process of claim 1, wherein: the at least one feed zone comprises: at least one addition section, at least one squeeze section, and at least one input section, wherein: the water-containing first component of the thermoplastic molding composition is introduced in the at least one addition section, the water-containing first component of the thermoplastic molding composition is to some extent dewatered in the at least one squeeze section, and the second component of the thermoplastic molding composition is introduced in the at least one input section.

6. The process of claim 5, wherein at least a portion of a barrel section of the input section is heated by temperature-control equipment in a manner such that the temperature of the portion of the barrel section of the input section is higher than the temperature of at least one portion of the mixing barrel section.

7. The process of claim 5, wherein the water-containing first component introduced in the at least one addition section is a rubber.

8. The process of claim 7, wherein the rubber comprises at least one polybutadiene.

9. The process of claim 7, wherein the rubber comprises at least one acrylate rubber.

10. The process of claim 5, wherein the second component introduced in the at least one input section is a styrene-acrylonitrile copolymer (SAN).

11. The process of claim 5, wherein the second component is introduced as melt in the at least one input section.

12. The process of claim 2, wherein the temperature at which at least one mixing barrel section is maintained is lower by at least 20 K than the temperature of the thermoplastic molding composition within the mixing section.

13. The process of claim 9, wherein the rubber comprises at least one butyl acrylate rubber.

Description

(1) Embodiments of the invention are explained in more detail on the basis of the drawing below, of the description below and of the claims.

(2) FIG. 1: is a diagrammatic sectional depiction of an extruder.

(3) An extruder 10 depicted diagrammatically in FIG. 1 is configured here as twin-screw extruder. The extruder 10 here has two extruder screws rotating around parallel axes.

(4) The two extruder screws here are arranged within an elongate barrel of the extruder 10. The extruder 10 serves for the production of thermoplastic molding compositions, in particular acrylonitrile-butadiene-styrene (ABS) or acrylonitrile-styrene-acrylate (ASA).

(5) In the direction of conveying, viewed in downstream direction, the extruder 10 has an addition section 22, a squeeze section 24, an input section 26, a mixing section 30, a venting section 40 and a discharge zone 50. The individual sections and zones of the extruder 10 here have barrel sections connected to one another by means of flanges.

(6) The addition section 22 of the extruder 10 serves for the introduction of a water-containing first component of the required thermoplastic molding composition. The squeeze section 24 of the extruder 10 serves for the partial dewatering of the first component of the thermoplastic molding composition. The input section 26 of the extruder 10 serves for the introduction of a second component of the required thermoplastic molding composition.

(7) The squeeze section 24 here is not essential. The dewatering can also by way of example take place in the mixing section 30. The input section 26 is moreover not essential. The second component of the thermoplastic molding composition can also be introduced into the extruder 10 together with the first component of the thermoplastic molding composition in the addition section 22.

(8) The addition section 22, the squeeze section 24 and the input section 26 together form a feed zone 20 of the extruder 10. The feed zone 20 here has, with the addition section 22 and the input section 26, two sections for the introduction of components of the required thermoplastic molding composition. It is also possible that the feed zone 20 has only one such section serving for the introduction of all of the components of the required thermoplastic molding composition. The feed zone 20 of the extruder 10 therefore serves for the introduction of the water-containing thermoplastic molding composition.

(9) The mixing section 30 of the extruder 10 serves for the mixing of the thermoplastic molding composition. During the mixing procedure, water present in the thermoplastic molding composition is also evaporated. The venting section 40 of the extruder 10 has a venting aperture through which water vapor can escape, thus being removed from the thermoplastic molding composition.

(10) The discharge zone 50 of the extruder 10 serves for the discharge of the thermoplastic molding composition from the extruder 10. For this, the discharge zone 50 has a pelletizing die 60 which has a plurality of perforations. When the thermoplastic molding composition is discharged from the discharge zone 50 here, it is forced through the perforations of the pelletizing die 60. The discharge zone 50 can also have a die plate instead of the pelletizing die 60.

(11) The addition section 22, the squeeze section 24, the input section 26, the mixing section 30, the venting section 40 and the discharge zone 50 respectively have barrel sections which can be temperature-controlled, in particular can be heated, by means of external temperature-controlled equipment not depicted here. Said external equipment here can be electrically operated heating equipment or else heating equipment through which a liquid flows, or else cooling equipment.

(12) The mixing section 30 here has a first mixing barrel section 31 and a second mixing barrel section 32. The first mixing barrel section 31 of the mixing section 30 here is situated upstream and adjoins the input section 26. The second mixing barrel section 32 of the mixing section 30 is situated downstream and adjoins the venting section 40.

(13) The individual items of external temperature-control equipment here can be operated independently of one another. It is therefore possible to heat or cool the barrel sections of individual sections or zones of the extruder 10 in a controlled manner, while simultaneously there is no temperature-control of barrel sections via other sections or zones of the extruder 10. In particular, the first mixing barrel section 31 and the second mixing barrel section 32 of the mixing section 30 can be temperature-controlled independently of one another.

(14) For the production of the thermoplastic molding composition, the first component of the required thermoplastic molding composition, which comprises water, is introduced into the addition section 22 of the extruder 10. The first component here is a particulate rubber which has from 1 to 40% by weight water content, preferably from 20 to 35% by weight, in particular about 30% by weight.

(15) The rubber introduced into the addition section 22 is transported by the twin-screw system of the extruder 10 into the squeeze section 24. Partial dewatering of the rubber takes place in the squeeze section 24. The barrel section of the squeeze section 24 here is temperature-controlled, in particular cooled, by means of the temperature-control equipment not depicted.

(16) The second component of the required thermoplastic molding composition is introduced into the input section 26 of the extruder 10. The second component here is styrene-acyrIonitrile copolymer (SAN).

(17) The styrene-acrylonitrile copolymer (SAN) here is introduced as melt into the input section 26. The barrel section of the input section 26 here is heated by means of the heating equipment not depicted.

(18) The rubber here is transported by the twin-screw system of the extruder 10 from the squeeze section 24 into the input section 26 and mixed with the styrene-acrylonitrile copolymer (SAN) introduced into the input section 26 to give the thermoplastic molding composition. The thermoplastic molding composition is transported onward by the twin-screw system of the extruder 10 from the input section 26 into the mixing section 30. Further mixing of the thermoplastic molding composition takes place in the mixing section 30 of the extruder 10.

(19) The measured temperature of the thermoplastic molding composition within the mixing section 30 here is about 230 C. During the further mixing in the mixing section 30 of the extruder 10, water still present in the thermoplastic molding composition is evaporated. The water vapor produced by the evaporation passes out of the extruder 10 through a venting aperture provided in the venting section 40. The water vapor produced by the evaporation is thus removed from the thermoplastic molding composition.

(20) The thermoplastic molding composition is transported onward by the twin-screw system of the extruder 10 from the mixing section 30 into the venting section 40, where the water vapor produced is discharged from the extruder 10 through the venting aperture.

(21) From the venting section 40, the thermoplastic molding composition is transported onward by the twin-screw system of the extruder 10 to the discharge zone 50. In the discharge zone 50 the thermoplastic molding composition is discharged from the extruder 10. The thermoplastic molding composition is forced out of the extruder 10 through the perforations in the pelletizing die 60.

(22) The thermoplastic molding composition discharged from the extruder 10 is then pelletized in a pelletizer unit not depicted here. The pelletization here preferably takes the form of underwater pelletization. In this procedure, the filaments emerging from the perforations 60 on the pelletizing die 50 are chopped to a prescribed length by means of a rotating blade. The blade, and also the emerging filaments, are located here in a water chamber. The chopping procedure thus produces pellets. It is also possible, as an alternative, to carry out strand pelletization in a water bath. The examples and claims provide explanation of the invention.

(23) In a process known from the prior art for the production of a thermoplastic molding composition, the first mixing barrel section 31 and the second mixing barrel section 32 of the mixing section 30 are heated to a temperature of about 240 C. This gives an average operating time of 15 days. The operating time here is the time during which the extruder 10 produces the thermoplastic molding composition without interruption.

(24) The operating time here ends when the perforations in the pelletizing die 60 or the perforations in the die plate of the extruder 10 are to some extent or entirely blocked, and the pelletizing die 60 or the die plate requires cleaning.

(25) In a first experiment for the production of a thermoplastic molding composition, the first mixing barrel section 31 of the mixing section 30 is heated to a temperature of about 240 C. The second mixing barrel section 32 is operated adiabatically. This gives an operating time of about 30 days.

(26) In a second experiment for the production of a thermoplastic molding composition, the second mixing barrel section 32 of the mixing section 30 is heated to a temperature of about 240 C. The second mixing barrel section 31 is operated adiabatically. This likewise gives an operating time of 30 days.

(27) In a third experiment for the production of a thermoplastic molding composition, the first mixing barrel section 31 and the second mixing barrel section 32 of the mixing section 30 are operated adiabatically. This gives an operating time of 40 days.

(28) In a fourth experiment for the production of a thermoplastic molding composition, the first mixing barrel section 31 of the mixing section 30 is temperature-controlled to a temperature of about 200 C. The second mixing barrel section 32 is likewise temperature-controlled to a temperature of about 200 C. This gives an operating time of 45 days. In a fifth experiment for the production of a thermoplastic molding composition, the first mixing barrel section 31 of the mixing section 30 is temperature-controlled to a temperature of about 200 C. The second mixing barrel section 32 is temperature-controlled to a temperature of about 240 C. This gives an operating time of 40 days.

LIST OF REFERENCE SIGNS

(29) 10 Extruder

(30) 20 Feed zone

(31) 22 Addition section

(32) 24 Squeeze section

(33) 26 Input section

(34) 30 Mixing section

(35) 31 First mixing barrel section

(36) 32 Second mixing barrel section

(37) 40 Venting section

(38) 50 Discharge zone

(39) 60 Pelletizing die